1. Field of the Invention
The present invention relates to a fixing device and a fixing method in which an image is fixed onto a recording material while supplying power to a heating part of a fixing roller from a storage unit.
2. Discussion of the Related Art
A fixing device that fixes a toner image formed on a recording material such as a recording sheet, via a heating part having a main heating element and an auxiliary heating element has been widely used. In such a conventional fixing device, the main heating element is powered by a main power supply unit, and the auxiliary heating element is powered by an auxiliary power supply unit including a capacitor. When the heating part starts to generate heat, the amount of power supplied from the capacitor to the auxiliary heating element is adjusted based on the temperature of the heating part.
Published Japanese patent application No. 2002-184554 describes the above fixing device. In the fixing device, the heating part is rapidly warmed-up to a predetermined temperature by being supplied with a large amount of power from both the main power supply unit and the auxiliary power supply unit. During a stand-by state of the fixing device, the main power supply unit and the auxiliary power supply unit do not supply power to the heating part. Thus, the power-saving effect is enhanced, and the noise caused by a sudden current change or an in-rush current at the time of starting or stopping the supply of high power is reduced. Further, a warm-up time of the heating part is reduced, and the heating part is prevented from overheating. The fixing device further includes a charger, a switching unit, a temperature detecting unit, and a control unit. The charger charges the capacitor of the auxiliary power supply unit with power supplied from the main power supply unit. The switching unit performs switching between the charger of the auxiliary power supply unit and the supply of power from the auxiliary power supply unit to the auxiliary heating element. The temperature detecting unit detects the temperature of the heating part. The control unit controls the amount of power supplied from the auxiliary power supply unit to the auxiliary heating element based on the temperature of the heating part detected by the temperature detecting unit.
In another known fixing device including a fixing member and a pressing member disposed opposite to the fixing member, a toner image formed on a recording material is fixed by heat and pressure while the recording material passes through a nip part between the fixing member and the pressing member. At a startup period of the fixing device during which the fixing member is heated until the temperature of the fixing member reaches a target temperature, the fixing member and the pressing member are pre-rotated to make the temperatures of these members uniform before starting a fixing operation of a toner image. For example, Published Japanese patent application No. 2002-82570 describes a fixing device in which a fixing member and a pressing member are pre-rotated.
In a fixing device using a main power supply unit and an auxiliary power supply unit including a capacitor that supplies power to a heating part, it is desirable to efficiently save the power supplied to the heating part from the auxiliary power supply unit and to enhance a quality of an image fixed on a recording material even if the fixing device is in a low temperature condition.